This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-088325, filed on Mar. 27, 2002, the entire contents of which are incorporated herein by reference.
The present invention relates to a booster for boosting an input voltage to generate a boosted voltage and to an imaging device provided with a booster.
In electronic equipment that requires different voltages, boosting circuits or regulating circuits are used to obtain multiple voltages from the same power supply. FIG. 1 is a schematic block diagram illustrating part of the configuration of an imaging device 50 in such electronic equipment.
The imaging device 50 includes a boosting circuit 1, a regulating circuit 2, a CCD driver circuit 3, and a CCD image sensor 4. The boosting circuit 1 boosts a power supply voltage VD, which is received by its input terminal, to generate a boosted voltage VO1 and outputs the boosted voltage VO1. The boosting circuit 1 includes, for example, a charge pump circuit, which has a plurality of transistors connected in series between the input terminal and an output terminal, and a capacitor, which has a terminal connected to a node between adjacent transistors.
The regulating circuit 2 receives the boosted voltage VO1 from the boosting circuit 1 to generate a predetermined adjusted voltage VO2. The regulating circuit 2 resistor-divides the boosted voltage VO1 to generate a divisional voltage and compares the divisional voltage with a predetermined reference voltage VR. The regulating circuit 2 controls the adjusted voltage output in accordance with the result of the comparison. In the regulating circuit 2, the voltage value of the adjusted voltage is set in accordance with the operational voltage of the CCD driver circuit 3 in the next stage. The regulating circuit 2 decreases the boosted voltage VO1 to the operational voltage of the CCD driver circuit 3 to generate a suitably adjusted voltage VO2.
The CCD driver circuit 3 receives the adjusted voltage VO2 and generates clock pulses, which are in synchronism with a vertical synchronizing signal VT and a horizontal synchronizing signal HT, which are provided from a timing control circuit (not shown). The generated clock pulses are provided to the CCD image sensor 4.
The CCD image sensor 4 has a light-receiving section, which includes a matrix of light-receiving pixels. The CCD image sensor 4 receives the light entering the light-receiving section with each light-receiving pixel and performs photoelectric conversion to generate information charges. The CCD image sensor 4 stores the information charges in each light-receiving pixel for a predetermined storage time. Then, the CCD image sensor 4 sequentially transfers the information charges in accordance with the clock pulses from the CCD driver circuit 3. An output section, which is located in the final stage of a transfer route, converts the information charges to a voltage value to generate an image signal Y(t). The image signal Y(t) undergoes a predetermined signal process in an analog signal processing circuit and a digital signal processing circuit (not shown), which are in the following stage, to provide a storage medium or a display device with data representing image information.
The boosted voltage VO1 of the boosting circuit 1 depends on the power supply voltage VD and fluctuates in accordance with the fluctuation of the power supply voltage VD. Thus, if the power supply voltage VD decreases unexpectedly for one reason or another, the boosted voltage VO1 also follows the decrease in the power supply voltage VD and decreases. Accordingly, the CCD driver circuit 3 may not be supplied with the required operational voltage. In such a case, there may be a problem in the imaging operation of the imaging device 50.
Further, the boosted voltage VO1 is dependent on fluctuation of the current flowing through a load, which is operated by the boosted voltage VO1. Thus, when a large amount of current is consumed in the load, the boosted voltage VO1 changes in accordance with the large current consumption. In such a case, it may be difficult to guarantee suitable operational voltage output for the CCD driver circuit 3.
One aspect of the present invention is a booster for receiving a power supply voltage and generating a boosted voltage. The booster includes a charge pump circuit including a plurality of boosting units connected in series and selectively validating the boosting units to generate the boosted voltage in accordance with the number of validated boosting units. A boost control circuit is connected to the charge pump circuit to determine whether the boosted voltage is in a predetermined range and change the number of validated boosting units in accordance with the determination.
A further aspect of the present invention is a method for controlling a charge pump circuit including a plurality of boosting units that are connected in series. The boosting units are selectively validated to generate the boosted voltage in accordance with the number of validated boosting units. The method includes generating a divisional voltage by dividing the boosted voltage, determining whether the divisional voltage is in a predetermined range, and changing the number of boosting units that are validated in accordance with the determination.
A further aspect of the present invention is an imaging device including a solid state imaging device having a plurality of light receiving pixels for storing information charges and a charge pump circuit including a plurality of boosting units connected in series for selectively validating the boosting units to generate a boosted voltage in accordance with the number of validated boosting units. A boost control circuit is connected to the charge pump circuit to determine whether the boosted voltage is in a predetermined range and change the number of validated boosting units in accordance with the determination. A regulating circuit is connected to the charge pump circuit to generate a predetermined adjusted voltage in accordance with the boosted voltage and a reference voltage. A drive circuit is connected to the regulating circuit to drive the solid state imaging device. The drive circuit is operated in accordance with the adjusted voltage for driving the solid state imaging device to obtain an image signal from the information charges.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.